IP telephony and VoIP are technologies that generally encompass one or more techniques for conducting communication sessions over the Internet. In some instances, the communication sessions are between client applications being executed by computing devices, where the communication sessions include one or more audio and/or video streams. The communication sessions may be conducted using one or more communication protocols including, but not limited to, Transmission Control Protocol (TCP), Internet Protocol (IP), User Datagram Protocol (UDP), H.323, the Session Initiation Protocol (SIP), the Real-time Transport Protocol (RTP), the Skype Protocol, or combinations thereof (e.g., SIP over TCP).
Using a computing device and the client application, a user may establish a communication with another computing device executing the same, or similar client application. Further still, the user may establish a communication session with a device communicatively coupled to a different network than the computing device the user is using to conduct the communication session. For example, the computing device may be communicatively coupled to a packet-switched network, such as the Internet. Alternatively, an intended recipient (or second computing device) may be communicatively coupled to a circuit-switched network, such as the public switched telephone network (PSTN).
In some instances a user may desire to call a public service, such as an emergency service, using his or her computing device. Using the client application, the user may attempt to establish a communication session with the public service, where the public service is communicatively coupled to the PSTN. However, the user may be prohibited or prevented from establishing the communication session with the public service using the computing device.